With respect, that time for the G55 from 0-200kph is that of a standard 500hp model with the V8 Kompressor engine.
The G55 with the SLR engine should be a bit quicker
However, in any event, the Brabus V12 G-Wagen should be the quickest G-Class. I don't have figures but if you have heard of MB's TT V12's + Brabus tuning; then nothing more needs to be said.
(Just look at the takeoff at 2.55)
http://www.youtube.com/watch?v=9tIf4Aqfb4c